Polychlorinated biphenyls (PCBs) and the DDT family are toxic, widespread hydrocarbons that are poorly understood in terms of their toxicity for human beings. In addition to their direct toxicity, both of these chemicals pass from mother to child through the placenta and by contaminating breast milk. This project includes a study of subjects exposed to low levels of these compounds in the US and a study of subjects exposed to higher doses in Taiwan. The Breast milk and Formula study is a birth cohort follow up study of 856 North Carolina children. PCBs and DDE (the stored metabolite of DDT) are measured in breast milk and the children are followed medically over time. Most of the children have completed 5 years of observation and are now followed only by a birthday car registry. We had seen that women with higher levels of DDE breast feed for shorter lengths of time, and were able to show that there was not increased morbidity due to chemical contamination of milk. This makes it more likely that lactation is suppressed in the mother, perhaps by the estrogenic properties of DDE. An epidemic of 2000 cases of PCB poisoning occurred in Taiwan in 1979. Rice oil was accidentally contaminated during manufacture. We did a survey of 117 children who were born to mothers who were poisoned, 40 of their older siblings, and 107 controls. All children received a physical examination and the mothers answered a questionnaire about their children's health. Children exposed in utero are lighter, shorter, and have smaller head circumference. They are more frequently pigmented, with dysplastic nails, have abnormal teeth, and are developmentally delayed.